Light guide plate, lighting apparatus and liquid crystal display provided with the same, and light guide plate molding die

ABSTRACT

A light guide plate includes at least one surface including a first region having relatively small surface roughness and a second region having relatively great surface roughness, which are adjacently formed. A boundary-blurring pattern composed of a plurality of surface roughness aspects is formed in a boundary part between the first region and the second region.

CLOSS REFERENCE TO RELATED APPLICATION

This Nonprovisional application claims priority under 35 U.S.C. §119 (a)on Patent Application No. 2003-394193 filed in Japan on Nov. 25, 2003and Patent Application No. 2004-295122 filed in Japan on Oct. 7, 2004,the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light guide plate used in a lightingapparatus such as a backlight of a liquid crystal display, a lightingapparatus and a liquid crystal display provided with it, and a lightguide plate molding die.

2. Description of the Prior Art

According to a backlight of a liquid crystal display, a reflection sheetis provided on a reflection side of a light guide plate, and a prismsheet and a diffusion sheet or a polarized light reflection sheet arelaminated on a light emission side thereof in general. Light input froma side end of the light guide plate is uniformly emitted from its lightemission surface to uniformly irradiate a liquid crystal display panelprovided in front of the diffusion sheet or the polarized lightreflection sheet. According to the light guide plate, protrusions areformed on the reflection surface (on the side of the reflection sheet)and the light emission surface with predetermined surface roughness toadjust direction and spread, or luminance and uniformity of the lightemitted from the light emission surface.

Japanese Unexamined Patent Publication No. 10-188642 discloses a lightguide plate having a reflection pattern which reflects light diffusely,in which a first reflection pattern is provided on one surface of thelight guide plate and a second reflection pattern is provided so as notto be overlapped with the first reflection pattern on the other surfaceof the light guide plate, in a lighting apparatus for performing surfaceillumination such as a backlight. This document further discloses thatsince the reflection patterns are provided so as not to be overlappedwith each other, light diffused and reflected by each reflection patternis emitted from slits of the reflection pattern on the opposite sidesurface, so that illumination can be performed from both sides of theone light guide plate.

Japanese Unexamined Patent Publication No. 2002-169033 discloses adirectional light guide plate in which light from an end face is emittedeach of front and back surfaces, many fine spherical protrusions areprovided on a side of a light emission surface, and a prism iscontinuously provided on the opposed surface in the directionperpendicular to the light entrance surface, and in which a diffusionprotrusion pattern having small angular protrusions which aresuperimposed in a region having relatively low luminance on the lightemission surface. This document discloses that with the directionallight guide plate, a uniform and high-luminance surface light source fora large screen can be implemented.

By the way, the light guide plate is molded by injection molding ingeneral and the protrusions are formed by transferring recesses formedon a molding surface of an insert die provided in the die. Here, therecesses of the insert die are formed by a sand blasting method and thelike. More specifically, the entire surface of the insert die issandblasted lightly first in order to adjust luminance and uniformity ascharacteristics of the light guide plate to be molded, and then a partin which surface roughness is needed to be more rough is sandblastedagain.

The recesses are formed in the insert die at parts in which the surfaceroughness of the insert die corresponds to the surface roughness of thelight guide plate which is a molded product. However, in the case wherethe recesses are formed by the method described above, when light isemitted from the molded light guide plate, luminance ununiformity isgenerated at a boundary part in which the surface roughness changes andthis appears on a display screen of the liquid crystal display.

Japanese Unexamined Patent Publication No. 2003-39487 discloses a methodfor forming a gradation pattern of protrusions on a molding surface ofan insert die of a light guide plate molding die, by projecting a shotblasting material into strips on the surface of an insert die of thelight guide plate molding die at a controlled pressure in parallel, inwhich a difference in protrusion forming pressure variation is to be notmore than 0.02 MPa in a part between adjacent blast bands havingdifferent diameters and depths of the protrusions. This documentdiscloses that ununiformity is not generated at a boundary part betweenblast bands because of the gradation pattern by the protrusions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light guide platein which luminance ununiformity is not generated at a boundary part inwhich surface roughness changes, a lighting apparatus and a liquidcrystal display provided with it, and a light guide plate molding die.

A light guide plate according to the present invention to attain theabove object includes at least one surface including a first regionhaving relatively small surface roughness and a second region havingrelatively great surface roughness, which are adjacently formed. Aboundary-blurring pattern composed of a plurality of surface roughnessaspects is formed in a boundary part between the first region and thesecond region.

Here, the surface roughness may be arithmetic average roughness (Ra),average height (Ry) or ten-point average roughness (Rz).

The surface roughness aspect is a surface aspect which appearscorresponding to surface roughness of the first region or the secondregion in the light guide plate. For example, when the surface roughnessis small, the surface roughness aspect is a surface which is close to amirror surface and when the surface roughness is great, the surfaceroughness aspect is a course surface.

As the boundary-blurring pattern, there are a checkered pattern, amosaic pattern, and a concavo-convex mesh pattern along the boundarypart between the first region and the second region.

The light guide plate of the present invention can be used in abacklight provided on a back side of a liquid crystal display panel as alight valve in a lighting apparatus or a liquid crystal display whichconstitutes a surface light source.

The light guide plate of the present invention is manufactured by theinjection molding, for example. A light guide plate molding die used inthe injection molding is subjected to a surface treatment on its moldingsurface corresponding to the surface having the first and second regionsof the light guide plate in such a manner that a boundary-blurringpattern composed of a plurality of surface roughness aspects is formedin a boundary part between the first region and the second region of thelight guide plate.

Here, as the surface treatment, there is a sand blasting method, forexample.

BRIEF DESCRIPTION OF THE DRAWINGS

These objects and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

FIG. 1 is a perspective view showing a liquid crystal display accordingto an embodiment 1.

FIG. 2 is a perspective view showing a light guide plate according tothe embodiment 1.

FIG. 3 is a plan view showing a boundary part between a first region anda second region on a surface of the light guide plate according to theembodiment 1.

FIG. 4 is a plan view showing a boundary part of a first region and asecond region on a surface of a light guide plate in which aboundary-blurring pattern is not provided.

FIG. 5 is a sectional view showing a light guide plate molding dieaccording to the embodiment 1.

FIG. 6 is a plan view showing a boundary part between a first region anda second region on a surface of a light guide plate according to anembodiment 2.

FIG. 7 is a plan view showing a boundary part between a first region anda second region on a surface of a light guide plate according to avariation of the embodiment 2.

FIG. 8 is a plan view showing a boundary part between a first region anda second region on a surface of a light guide plate according to anembodiment 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Light Guide Plate, Lighting Apparatus, Liquid Crystal Display, andLight Guide Plate Molding Die)

A light guide plate according to an embodiment of the present inventionincludes at least one surface including a first region having relativelysmall surface roughness and a second region having relatively greatsurface roughness which are adjacently formed, in which aboundary-blurring pattern composed of a plurality of surface roughnessaspects is formed in a boundary part between the first region and thesecond region.

According to this light guide plate, since the boundary-blurring patternis constituted in the boundary part between the first region and thesecond region, the surface roughness is not largely suddenly changed inthe boundary part between the first region and the second region, sothat the change in surface roughness can become moderate in the boundarypart between the first region and the second region by theboundary-blurring pattern. Therefore, when the light from the lightsource is emitted from the light guide plate, luminance ununiformity canbe prevented from being generated in the boundary part in which thesurface roughness changes.

Here, the surface roughness may be arithmetic average roughness (Ra),average height (Ry) or ten-point average roughness (Rz).

The surface roughness aspect is a surface aspect which appearscorresponding to surface roughness of the first region or the secondregion in the light guide plate. For example, when the surface roughnessis small, the surface roughness aspect is a mirror surface and when thesurface roughness is great, the surface roughness aspect is a coursesurface.

As the boundary-blurring pattern, there are a checkered pattern, amosaic pattern, and a concavo-convex mesh pattern along the boundarypart between the first region and the second region.

When the boundary-blurring pattern is the checkered pattern, thecheckered pattern is preferably constituted by the surface roughnessaspect of the first region and the surface roughness aspect of thesecond region.

The light guide plate is generally manufactured by the injection moldingand in order to form the surface roughness of the first and secondregions and the boundary part thereof, it is necessary to perform asurface treatment on a corresponding molding surface of a molding die bya sand blasting method and the like. In the case of the checkeredpattern as described above, since the surface treatment at the partcorresponding to the boundary part can be performed only by performing asurface treatment for forming the first region and a surface treatmentfor forming the second region, the surface treatment of the light guideplate molding die can be simplified.

When the boundary-blurring pattern is the mosaic pattern, the mosaicpattern is preferably composed of a plurality of surface roughnessaspects between the surface roughness aspect of the first region and thesurface roughness aspect of the second region.

In the case of the mosaic pattern as described above, when the surfacetreatment of the light guide plate molding die is performed by the sandblasting method, it suffices to perform plural steps of surfacetreatment only from the surface treatment for forming the first regionto the surface treatment for forming the second region step by step.

When the boundary-blurring pattern is the concavo-convex mesh pattern,the concavo-convex mesh pattern is preferably composed of the surfaceroughness aspect of the first region and the surface roughness aspect ofthe second region.

In the case of the concavo-convex mesh pattern as described above, sincethe surface treatment at the part corresponding to the boundary part canbe performed only by performing a surface treatment for forming thefirst region and a surface treatment for forming the second region, thesurface treatment of the light guide plate molding die can besimplified.

The light guide plate can be used in a backlight provided on a back sideof a liquid crystal display panel as a light valve in a lightingapparatus or a liquid crystal display which constitutes a surface lightsource.

The light guide plate is manufactured by the injection molding, forexample. A light guide plate molding die used in the injection moldingis subjected to a surface treatment on its molding surface correspondingto the surface having the first and second regions of the light guideplate in such a manner that a boundary-blurring pattern composed of aplurality of surface roughness aspects is formed in a boundary partbetween the first region and the second region of the light guide plate.

(Concrete Constitution)

Hereinafter, preferred embodiments will be described with reference tothe accompanying drawings.

Embodiment 1

FIG. 1 is a view showing a liquid crystal display 100 according to anembodiment 1 of the present invention.

The liquid crystal display 100 includes a liquid crystal display panel110 and a backlight (lighting apparatus) 120 provided on its back side.

The liquid crystal display panel 110 in which a liquid crystal layer issandwiched by a pair of substrates functions as a light valve.

The backlight 120 has a cuneiform light guide plate 121 made of atransparent acrylic resin (PMMA), for example and a cold cathodefluorescent lamp 122 is provided at a thicker side end of the lightguide plate 121. The cold cathode fluorescent lamp 122 is held by arubber holder 123 for a light source and a reflection sheet 124 isprovided so as to surround it and cover a back surface of the lightguide plate 121, that is, an non-emission surface. A prism sheet 125 anda diffusion sheet 126 are provided so as to be laminated on a frontsurface, that is, the side of an emission surface of the light guideplate 121. The backlight 120 functions as a surface light source whichemits uniform light from the emission surface of the light guide plate121 to the liquid crystal display panel 110.

FIG. 2 is a view showing the light guide plate 121.

The light guide plate 121 has predetermine surface roughness on a frontsurface which is the emission surface and/or a back surface which is thenon-emission surface. More specifically, a first region 10 is formed onan almost entire surface of the light guide plate 121 in which regularsized protrusions are provided at a predetermined density so as to haverelatively small surface roughness, and a second region 20 is formed ina part having a small amount of light guided from the cold cathodefluorescent lamp 122 so as to have relatively great surface roughness toincrease reflection and diffusion of the light. The second region 20includes a part 121 a in the vicinity of the thick end face in whichreflection and diffusion of light is insufficient, a part 121 b in thevicinity of a thin end face in which an absolute amount of the light isinsufficient, a part 121 c at both corners on the thick side in which alight guided amount is insufficient in the presence of the light sourcerubber holder 123, and the like. Here, the surface roughness meansarithmetic average roughness (Ra), average height (Ry) or ten-pointaverage roughness (Rz).

FIG. 3 is a view showing a surface of the light guide plate 121.

A boundary-blurring pattern formed by arrangement of a plurality ofsurface roughness aspects, that is, surface aspects which appearcorresponding to the surface roughness is constituted in a boundary part30 between the first region 10 and the second region 20. Morespecifically, the boundary-blurring pattern is a checkered pattern ofsurface roughness aspect A of the first region 10 and surface roughnessaspect B of the second region 20 in which each element is of 2 mm to 3mm square, as shown in FIG. 3.

According to this light guide plate 121, since the checkeredboundary-blurring pattern is constituted in the boundary part 30 betweenthe first region 10 and the second region 20, the surface roughness isnot largely suddenly changed at the boundary part 30 between the firstregion 10 and the second region 20 as shown in FIG. 4, so that thechange in surface roughness can become moderate at the boundary part 30between the first region 10 and the second region 20 by theboundary-blurring pattern. Therefore, even when the light from the lightsource is emitted from the light guide plate 121, luminance ununiformitycan be prevented from being generated at the boundary part 30 in whichthe surface roughness changes.

This light guide plate 121 can be manufactured by the injection molding.

FIG. 5 is a view showing a light guide plate molding die 200 for moldingthe light guide plate 121.

The light guide plate molding die 200 includes a cavity 210corresponding to an outline of the cuneiform light guide plate 121, andan inner die 220 is provided so as to correspond the front surfaceand/or back surface of the light guide plate 121 (only the inner die 220for molding one surface of the light guide plate 121 is shown in FIG.5). On the molding surface of the inner die 220, a surface treatment toform many recesses has been performed so that the protrusions on thesurface of the light guide plate 121 may be molded. More specifically,the entire molding surface is sandblasted so that surface roughness maybecome No. 400 or less, for example, and then, the part corresponding tothe first region 10 and a part corresponding to the surface roughnessaspect A of the first region 10 in the boundary part 30 are masked, andan exposed part, that is, a part corresponding to the second region 20and a part corresponding to the surface roughness aspect B of the secondregion 20 in the boundary part 30 are sandblasted again such that thesurface roughness may become No. 20 or more, for example. Since theboundary part 30 is constituted by the checkered pattern which consistsof the surface roughness aspect A of the first region 10 and the surfaceroughness aspect B of the second region 20, in the above light guideplate 121, the surface treatment at the boundary part can be performedonly by performing the surface treatment for forming the first region 10and the surface treatment for forming the second region 20.

The above light guide plate molding die 200 is mounted on an end of anozzle of an injection molding machine, and a molten resin from theinjection molding machine is filled in the cavity 210 and cooled down,whereby the light guide plate 121 having the above constitution on whichthe molding face of the inner die 220 is transferred is provided.

Embodiment 2

A liquid crystal display according to an embodiment 2 of the presentinvention is the same as the embodiment 1 except for a constitution of alight guide plate 121. The same reference numerals denote the samecomponents as in the embodiment 1.

FIG. 6 is a view showing a surface of the light guide plate 121.

A boundary-blurring pattern formed by arrangement of a plurality ofsurface roughness aspects, that is, surface aspects which appearcorresponding to the surface roughness is constituted in a boundary part30 between the first region 10 and the second region 20. Morespecifically, the boundary-blurring pattern is a mosaic pattern ofsurface roughness aspect A of the first region 10, surface roughnessaspect B of the second region 20 and surface roughness aspect C of amiddle of them in which each element is of 2 mm to 3 mm square. Theother constitutions and working effects are the same as in the lightguide plate 121 in the embodiment 1. In addition, the mosaic pattern isnot limited to the one shown in FIG. 6 and it may be a pattern shown inFIG. 7.

On a molding surface of an insert die 220 of a light guide plate moldingdie for molding the above light guide plate 121, a surface treatment forforming many recesses is performed so as to correspond to protrusions onthe surface of the light guide plate 121 to be molded. Morespecifically, the entire molding surface is sandblasted to be rough at alow level, and then a part corresponding to the first region 10 and apart corresponding to the surface roughness aspect A of the first region10 in the boundary part 30 are masked, and an exposed part issandblasted again so as to be rough at a middle level. Then, a partcorresponding to the middle surface roughness aspect C is masked, and anexposed part, that is, a part corresponding to the second region 20 anda part corresponding to the surface roughness aspect B of the secondregion 20 in the boundary part 30 is sandblasted so as to be rough at ahigh level. According to the light guide plate 121, since the boundarypart 30 is constituted by the mosaic pattern which consists of thesurface roughness aspect A of the first region 10, the surface roughnessaspect B of the second region 20 and the surface roughness aspect C ofthe middle of them, the surface treatment for forming the first region10 and the surface treatment for forming the second region 20 only haveto be performed step by step. The other constitutions and a moldingmethod of the light guide plate 121 are the same as in the embodiment 1.

Embodiment 3

A liquid crystal display according to an embodiment 3 of the presentinvention is the same as the embodiment 1 except for a constitution of alight guide plate 121. The same reference numerals denote the samecomponents as in the embodiment 1.

FIG. 8 is a view showing a surface of the light guide plate 121.

A boundary-blurring pattern composed of a plurality of surface roughnessaspects, that is, surface aspects which appear corresponding to thesurface roughness is formed in a boundary part 30 between a first region10 and a second region 20. More specifically, the boundary-blurringpattern is a concavo-convex mesh pattern along the boundary part 30between the first region 10 and the second region 20. According to thisconcavo-convex mesh pattern, the boundary part between the first region10 of a surface roughness aspect A and the second region 20 of a surfaceroughness aspect B is formed in the shape of rectangle, and tine-shapedconcavities and convexities of an edge of the first region 10 mesh withtine-shaped concavities and convexities of an edge of the second region20. This tine-shaped concavity and convexity has a width of 1 mm or lessor about 2 to 3 mm or 3 mm or more and a length of about 2 to 20 mm. Theother constitutions and a working effect are the same as in the lightguide plate 121 of the embodiment 1.

On a molding surface of an insert die of a light guide plate molding diefor molding the light guide plate 121, a surface treatment for formingmany recesses is performed corresponding to protrusions on a surface ofthe light guide plate 121 to be molded. More specifically, the entiremolding surface is sandblasted to the degree of surface roughness No.400 or less, for example and then a part corresponding the first region10 is masked and an exposed part, that is, a part corresponding to thesecond region 20 is sandblasted again to the degree of surface roughnessabout No. 20 or more, for example. According to the light guide plate121, since the boundary part 30 is constituted by the concavo-convexmesh pattern consisting of the surface roughness aspect A of the firstregion 10 and the surface roughness aspect B of the second region 20,the surface treatment for the boundary part can be performed only byperforming the surface treatment for forming the first region 10 and thesurface treatment for forming the second region 20. The otherconstitutions and a molding method of the light guide plate 121 are thesame as in the embodiment 1.

Another Embodiment

Although the light guide plate 121 is the cuneiform in the aboveembodiments 1 to 3, the present invention is not limited to this and itmay be in the shape of flat plate.

In addition, although the prism sheet 125 and the diffusion sheet 126are constituted in the above embodiments 1 to 3, a combination of thediffusion sheet, the prism sheet and a polarized light reflection sheetmay be used.

Furthermore, although the cold cathode fluorescent lamp 122 is used inthe above embodiments 1 to 3, the present invention is not limited tothis and it may be an LED or the like.

Still furthermore, although each element of the boundary-blurringpattern is in the shape of square in the above embodiments 1 and 2, thepresent invention is not limited to this and it may be in the shape ofrectangle.

In addition, although the boundary line between the first region 10 andthe second region 20 is concavo-convex mesh pattern formed in the shapeof rectangles in the embodiment 3, the present invention is not limitedto this and it may be a concavo-convex mesh pattern formed in the shapeof sinusoidal waveform or anther waveform.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A light guide plate comprising at least one surface including a firstregion having relatively small surface roughness and a second regionhaving relatively great surface roughness, which are adjacently formed,wherein a boundary-blurring pattern composed of a plurality of surfaceroughness aspects is formed in a boundary part between the first regionand the second region.
 2. The light guide plate of claim 1, wherein theboundary-blurring pattern is a checkered pattern.
 3. The light guideplate of claim 2, wherein the checkered pattern of the boundary-blurringpattern is composed of a surface roughness aspect of the first regionand a surface roughness aspect of the second region.
 4. The light guideplate of claim 1, wherein the boundary-blurring pattern is a mosaicpattern.
 5. The light guide plate of claim 4, wherein the mosaic patternof the boundary-blurring pattern is composed of a plurality of surfaceroughness aspects between a surface roughness aspect of the first regionand a surface roughness aspect of the second region.
 6. The light guideplate of claim 1, wherein the boundary-blurring pattern is aconcavo-convex mesh pattern along a boundary part between the firstregion and the second region.
 7. The light guide plate of claim 6,wherein the concavo-convex mesh pattern of the boundary-blurring patternis composed of a surface roughness aspect of the first region and asurface roughness aspect of the second region.
 8. A lighting apparatusprovided with a light guide plate, wherein the light guide platecomprises at least one surface including a first region havingrelatively small surface roughness and a second region having relativelygreat surface roughness, which are adjacently formed, and aboundary-blurring pattern composed of a plurality of surface roughnessaspects is formed in a boundary part between the first region and thesecond region.
 9. A liquid crystal display comprising: a liquid crystaldisplay panel as a light valve; and a backlight provided on a back sideof the liquid crystal display panel and having a light guide plate,wherein the light guide plate of the backlight comprises at least onesurface including a first region having relatively small surfaceroughness and a second region having relatively great surface roughness,which are adjacently formed, and a boundary-blurring pattern composed ofa plurality of surface roughness aspects is formed in a boundary partbetween the first region and the second region.
 10. A light guide platemolding die for molding a light guide plate comprising at least onesurface including a first region having relatively small surfaceroughness and a second region having relatively great surface roughness,which are adjacently formed, wherein a surface treatment is performed ona molding surface corresponding to the surface having the first andsecond regions of the light guide plate so as to form aboundary-blurring pattern composed of a plurality of surface roughnessaspects in a boundary part between the first and second regions of thelight guide plate.